DESCRIPTION: The Applicant is proposing to continue his studies of the structure of LRP, functional activity of this receptor, and modulation of expression. The Investigator has delineated some of the functions of this large ubiquitous cellular receptor, which intervenes in the internalization of some lipoproteins. In addition, the same receptor associates with a2-macroglobulin (a2M), and a2M-proteinase complexes and also with uPA and tPA of the fibrinolytic system. The major effort of this application is toward the characterization of the association of LRP with lipoprotein lipase and with b-VLDL and the biochemical reaction responsible for the internalization of this complex via the LRP receptor. Binding studies of LpL and of VLDL will be done using normal cell lines and cells deficient in LPR or LDL receptors. The contribution of other cellular surface components to the binding of ligands to LRP, such as proteoglycans, will also be analyzed by performing these studies in cells with low expression of proteoglycans. A second Aim consists of elucidating the role of RAP, a 30-kDa protein that associates with LRP and seems to modify its functional activity.In his third specific Aim, the Investigator is planning to study some of the regulatory mechanisms involved in the expression of LPR and RAP by cellular components of the vessel wall.